Sensor electrodes are utilized to detect and monitor various characteristics of a liquid, both hydrocarbon and aqueous based. During the processing or monitoring of these liquids, it is desirable, if not essential, to be aware of characteristics such as acidity levels, conductivity and the amounts of specific ions such as, for example, calcium, chloride, bromide, ammonium, cupric, lead, sodium, nitrate and potassium, to name a few. Therefore, pH, conductivity, ORP and specific ion sensor electrodes are utilized.
In order for these selective sensor electrodes to function properly and give accurate, consistent results, a system of one or more filters may be employed to prevent contaminants from reaching the electrode and forming deposits on it or otherwise compromising its ability to function properly.
Filters are used to block dispersed solids. The filters may be designed in a variety of pore sizes and materials, depending upon the application. Pore sizes from 0.1 micron to 300 microns are typically used, although large pore sizes are not excluded depending on application. Filter materials may be constructed of sintered stainless steel, ceramics, teflon, cellulose, and other polymers.
Adsorbents are useful in blocking both particulate matter and various dissolved or discontinuous phase emulsified materials, such as oils (for aqueous liquids). The adsorbents may be utilized in a range of particle sizes and materials. The particle size employed will depend on the amount of material used in the adsorbent bed, as flow through the bed will be affected. Adsorbents utilized will be from a broad range of materials sold commercially for chromatographic applications. Typical materials which would be utilized include Tenax.RTM., Porapak, Amberlite.RTM. XAD, activated carbon, selective ion exchange resins, etc.
Frequently, filters or adsorbents will incorporate specific activity in order to selectively remove certain dissolved compounds which, if allowed to reach the sensor electrode, would interfere with the electrode's ability to give an accurate reading of a desired compound or characteristic, because of its closely related chemical functionality to the interfering compound. Examples of such "interferences" include volatile amines for ammonia or the ammonium ion, volatile weak acids for carbon dioxide, chloride or bromide for the cupric ion, ammonium or silver for potassium and Na.sup.+, Cu.sup.++, Zn.sup.++, Fe.sup.++ and Ni.sup.++ for water hardness readings. Even sodium (in basic solution) interferes with accurate pH readings.
Once the selective becomes saturated with its targeted contaminant, additional contaminant particles in the liquid sample will then proceed to clog it up by deposition or otherwise interfere with an accurate reading of the desired compound or characteristic. It is then necessary to remove and replace the saturated filter, resulting in undesirable downtime of the sensor system. In some instances, the sensor electrode may itself be so badly fouled or contaminated that it, too, must be removed and either manually cleaned or replaced with a new one.
Some sensor electrode systems employ a backflush feature, whereby the flow of filtrate is reversed through the filter or adsorbent to force the contaminants back out through the intake route. This theoretically regenerates the filter but is useful only when the contaminant is a solid. An example of such a device is the Filtrate Master System, sold by TBI-Bailey.
Where the contaminants are solubilized or, as with aqueous filtrates, oily compounds are present, backflushing with the filtrate being tested is generally ineffective. It is an object of this invention to prolong the life of the sensor electrode, provide more analytical accuracy and precision in the presence of interferences and to prolong the service life of the selective filters or adsorbents by removing specific interferents therefrom.